Reactivity and the resulting power level of a nuclear boiling water reactor (BWR) is adjusted by moving control rods in the nuclear core. A large reactor uses about 185 such rods. Each rod is driven in or out of the core in discrete steps by a hydraulic drive mechanism, which, in a typical installation, is controlled by four solenoid valves in a hydraulic control unit.
A rod drive control system allows an operator to control these solenoid valves and, through them, the positioning of all the rods in the core. The basic function of the rod drive control system involves the operator's choice of a particular rod and the timed control of the solenoid valves to drive the rod in or out. The system returns status information from each hydraulic control unit.
Due to the nature and sophistication of nuclear reactor systems and their associated electronics, comprehensive testing equipment has been developed. Typically, such testing equipment is built into the system, and requires considerable space and complexity.
Numerous tests are performed by this equipment, including the status of control rod drive and instrumentation systems. These tests are impeded by several factors: first, the control rods may not normally be moved during shutdown plant conditions; second, the operator must monitor the tests at his or her control panel located some 200 to 500 feet from the valves and rods themselves; third, the response of the rods to control commands are complex signals which require sophisticated and highly expert knowledge to decipher.